Function composition - Faith and Brave

理解するのに時間がかかった・・・

まだfunction + bind, lambdaの組み合わせには慣れないな

#include <iostream>
#include <boost/function.hpp>
#include <boost/lambda/lambda.hpp>
#include <boost/lambda/bind.hpp>

using namespace std;
using namespace boost;
using namespace boost::lambda;

template <class R, class I, class S>
function<R(I)> compose(function<R(I)> f, function<I(S)> g)
{
    return bind(f, bind(g, _1));
}

template <class T, class Y>
function<T> operator*(function<T> f, function<Y> g)
{
    return compose(f, g);
}

int main()
{
    function<int(int)> inc(_1 + 1);
    function<int(int)> triple(_1 * 3);
    function<int(int)> square(_1 * _1);

    cout << (inc * triple)(2)    << " = 2 x 3 + 1"     << endl; // 7
    cout << (square * square)(3) << " = (3x3) x (3x3)" << endl; // 81

    return 0;
}